Lighting device

ABSTRACT

An object of the invention is to provide a lighting device which can suppress luminance nonuniformity in a light emitting region when the lighting device has large area. A layer including a light emitting material is formed between a first electrode and a second electrode, and a third electrode is formed to connect to the first electrode through an opening formed in the second electrode and the layer including a light emitting material. An effect of voltage drop due to relatively high resistivity of the first electrode can be reduced by electrically connecting the third electrode to the first electrode through the opening.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lighting device using a lightemitting element.

2. Description of the Related Art

A light emitting element is a self light emitting element and isattempted to be used as a lighting device. The light emitting element isa surface-emitting body, and a lighting device capable of emittingnear-natural light can be obtained by using the light emitting elementfor lighting.

The light emitting element has an anode, a cathode, and a layerincluding a light emitting material which provides luminescence(Electroluminescence) by applying an electric field thereto. A holeinjected from the anode is combined with an electron injected from thecathode in the layer including a light emitting material, therebyobtaining luminescence. Luminescence obtained from the layer including alight emitting material includes luminescence (fluorescence) that isobtained in returning from a singlet excited state to a ground state andluminescence (phosphorescence) that is obtained in returning from atriplet excited state to a ground state.

In a light emitting device using such a light emitting element, anelectrode in the direction of light emission needs to be transparent.However, a transparent conductive film which is typically used as atransparent electrode often has relatively high resistivity, and voltagedrop is caused in a portion away from a current supply terminal.Specifically, the lighting device is often intended to emit light fromthe entire surface at the same luminance; therefore, in-planenonuniformity of luminance becomes further noticeable.

When the lighting device has large area, luminance is lowered in aportion through which current is hard to flow. In other words, luminanceis nonuniform in a light emitting region of the lighting device. An ITOelectrode typically used as the anode has higher electrical resistancethan that of metal such as Al used as the cathode. Therefore, voltagedrop is caused in a portion away from a current supply terminal, whichresults in low luminance. In order to solve the problem, Reference 1reports a structure in which at least a portion of an anode is providedwith an auxiliary electrode having lower electrical resistance than thatof the anode (Reference 1: Japanese Patent Laid-Open No. 2004-134282).

In Reference 1, an auxiliary electrode is provided on a long side or ashort side of a light emitting element. When the lighting device haslarger area, luminance is lowered in a portion away from the auxiliaryelectrode (for example, in a central portion of the lighting device).However, the auxiliary electrode can only be partly provided, becauselight emitted from a light emitting layer cannot be extracted outsidewhen the auxiliary electrode is entirely provided on the anode in thestructure of Reference 1.

Since the lighting device is often intended to emit light from theentire surface at the same luminance, nonuniformity of luminance becomesfurther noticeable.

SUMMARY OF THE INVENTION

In view of the above-described problem, it is an object of the inventionto provide a lighting device having favorable luminance uniformity in alight emitting region when the lighting device has large area.

One feature of a lighting device of the invention is that a layerincluding a light emitting material is formed between a first electrodeand a second electrode, and a third electrode is formed to connect tothe first electrode through an opening formed in the second electrodeand the layer including a light emitting material.

In other words, the lighting device has a layer including a lightemitting material and a second electrode between a first electrode andan auxiliary electrode; the auxiliary electrode is formed opposite tothe first electrode with the second electrode therebetween; and thefirst electrode is electrically connected to the auxiliary electrodethrough an opening formed in the second electrode and the layerincluding a light emitting material. Note that the first electrode andthe second electrode need to be electrically insulated from each otherand the second electrode and the auxiliary electrode need to beelectrically insulated from each other.

More specifically, another feature of the invention is that a layerincluding a light emitting material provided with a first opening and asecond electrode provided with a second opening are arranged over afirst electrode formed of a transparent conductive film so that thesecond opening overlaps the first opening; and an insulating layerformed over the second electrode, covering the first opening, the secondopening, and the side of the second opening, and provided with a thirdelectrode to expose the first electrode and a third electrode formedover the insulating layer to be in contact with the first electrodethrough the first to third openings are formed.

Another feature of the invention according to the above structure isthat a plurality of openings is formed in a light emitting region of alighting device.

In the above structure, light emitted from the layer including a lightemitting material is emitted from the first electrode side. In otherwords, the first electrode transmits light and is formed of atransparent conductive film. Specifically, indium tin oxide (hereinafterreferred to as ITO), indium tin oxide containing silicon, indium oxidecontaining zinc oxide (ZnO) of 2% to 20%, or the like can be used.

Note that a low-resistivity material is preferably used as the auxiliaryelectrode. An effect of voltage drop due to relatively high resistivityof the first electrode can be reduced by using a low-resistivitymaterial.

In the above structure, the layer including a light emitting materialmay have a laminated structure of a plurality of layers each including alight emitting material.

Further in the above structure, a substrate for supporting the lightingdevice may be a flexible substrate.

In the above structure, no light is lost except in a connection portionof the auxiliary electrode and the first electrode because the auxiliaryelectrode is not placed in the direction of light emission. Therefore, amaterial, a thickness, or a formation position of the auxiliaryelectrode can be freely set.

In the case where the area of the connection portion of the auxiliaryelectrode and the first electrode is sufficiently small, the presence ofthe auxiliary electrode can be, for the most part, disregarded even whenseen from the side of light emission. Therefore, a plurality of openingscan be formed in a light emitting region of the lighting device.

According to the invention, a lighting device having favorable in-planeuniformity of luminance can be obtained. Since an auxiliary electrode isnot placed in the direction of light emission, little light is lost dueto the auxiliary electrode, and a material, a thickness, or a formationposition of the auxiliary electrode can be freely set.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are a cross-sectional view and a top view of a lightemitting region in a lighting device of the present invention,respectively.

FIGS. 2A to 2D show a method for manufacturing a lighting device of thepresent invention.

FIGS. 3A to 3C show a method for manufacturing a lighting device of thepresent invention.

FIGS. 4A to 4C show a method for manufacturing a lighting device of thepresent invention.

FIGS. 5A and 5B are a cross-sectional view and a top view of a lightemitting region in a lighting device of the present invention,respectively.

FIGS. 6A to 6C show a method for manufacturing a lighting device of thepresent invention.

FIGS. 7A and 7B show a method for manufacturing a lighting device of thepresent invention.

FIGS. 8A and 8B are a top view and a cross-sectional view of a lightingdevice of the present invention, respectively.

FIG. 9 shows an example of a device using a lighting device of thepresent invention.

FIGS. 10A to 10C show examples of a device using a lighting device ofthe present invention.

FIG. 11 shows an example of a layer including a light emitting materialin a lighting device of the present invention.

FIG. 12 shows an example of a layer including a light emitting materialin a lighting device of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiment modes of the present invention are described in detail withreference to drawings. However, the present invention is not limited tothe following description. As is easily known to a person skilled in theart, the mode and the detail of the invention can be variously changedwithout departing from the purpose and the scope of the presentinvention. Thus, the present invention is not interpreted while limitingto the following description of the embodiment modes.

Embodiment Mode 1

A structure of a lighting device of the invention is described withreference to FIGS. 1A and 1B. A lighting device shown in FIGS. 1A and 1Bis a bottom emission lighting device which emits light from a substrateside. Note that FIG. 1B is a top view of a light emitting region in alighting device of the invention and FIG. 1A is a cross-sectional view(taken along line A-A′ in FIG. 1B) of the vicinity of an opening in thelight emitting region.

In FIGS. 1A and 1B, a light transmitting substrate is used as asubstrate 101. Specifically, a light transmitting material such asglass, plastic, polyester resin, or acrylic resin can be used. Thesubstrate 101 may be flexible.

A transparent conductive film is formed over the substrate 101 as afirst electrode 102. For example, indium tin oxide (hereinafter referredto as ITO), indium tin oxide containing silicon, indium oxide containingzinc oxide (ZnO) of 2% to 20%, or the like can be used for thetransparent conductive film.

A layer including a light emitting material 103 is formed over the firstelectrode 102. A known material can be used for the layer including alight emitting material 103, and either a low molecular weight materialor a high molecular weight material can be used. A material for formingthe layer including a light emitting material may include not only theone formed of only an organic compound material but also the one partlycontaining an inorganic compound. The layer including a light emittingmaterial is formed by appropriately combining a hole injection layer, ahole transport layer, a hole blocking layer, a light emitting layer, anelectron transport layer, an electron injection layer, or the like. Thelayer including a light emitting material may be a single layer or havea laminated structure of a plurality of layers. FIG. 11 shows an exampleof a structure in which the layer including a light emitting materialincludes a hole injection layer, a hole transport layer, a lightemitting layer, an electron transport layer, and an electron injectionlayer. In FIG. 11, a first electrode (anode) 1101, a layer including alight emitting material 1102, and a second electrode (cathode) 1103 areformed over a substrate 1100. The layer including a light emittingmaterial 1102 includes a hole injection layer 1111, a hole transportlayer 1112, a light emitting layer 1113, an electron transport layer1114, and an electron injection layer 1115. Note that the layerincluding a light emitting material in a lighting device of theinvention is not limited to the structure of FIG. 11. Hereinafter,described is a specific material used for the hole injection layer, thehole transport layer, the light emitting layer, the electron transportlayer, and the electron injection layer.

As a hole injection material for forming the hole injection layer, aporphyrin-based compound is effective among other organic compounds, andphthalocyanine (hereinafter referred to as H₂-Pc), copper phthalocyanine(hereinafter referred to as Cu-Pc), or the like can be used. Further, achemically doped high molecular weight conductive compound can be used,such as polyethylene dioxythiophene (hereinafter referred to as PEDOT)doped with polystyrene sulfonate (hereinafter referred to as PSS). Abenzoxazole derivative and any one or more of TCQn, FeCl₃, C₆₀, andF₄TCNQ may be included.

As a hole transport material for forming the hole transport layer, anaromatic amine-based compound (in other words, the one having a benzenering-nitrogen bond) is preferably used. For example,N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(hereinafter referred to as TPD) or a derivative thereof such as4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (hereinafter referredto as α-NPD) is widely used. Also widely used is a star burst aromaticamine compound such as 4,4′,4″-tris(N-carbazolyl)-triphenyl amine(hereinafter referred to as TCTA),4,4′,4″-tris(N,N-diphenyl-amino)-triphenyl amine (hereinafter referredto as TDATA), or4,4′,4″-tris[N-(3-methylphenyl)-N-phenyl-amino]-triphenyl amine(hereinafter referred to as MTDATA).

As a light emitting material for forming the light emitting layer,various fluorescent pigments are specifically effective, in addition toa metal complex such as tris(8-quinolinolato)aluminum (hereinafterreferred to as Alq₃), tris(4-methyl-8-quinolinolato)aluminum(hereinafter referred to as Almq₃),bis(10-hydroxybenzo[h]-quinolinato)beryllium (hereinafter referred to asBeBq₂), bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(hereinafter referred to as BAlq),bis[2-(2-hydroxyphenyl)-benzoxazolate]zinc (hereinafter referred to asZn(BOX)₂), or bis[2-(2-hydroxyphenyl)-benzothiazolate]zinc (hereinafterreferred to as Zn(BTZ)₂).

In the case of forming the light emitting layer in combination with aguest material, the following material can be used as the guestmaterial: quinacridon, diethyl quinacridon (hereinafter referred to asDEQD), dimethyl quinacridon (hereinafter referred to as DMQD), rubrene,perylene, coumarin, coumarin 545T (hereinafter referred to as C545T),DPT, Co-6, PMDFB, BTX, ABTX, DCM, DCJT, or a triplet light emittingmaterial (phosphorescent material) such as tris(2-phenylpyridine)iridium(hereinafter referred to as Ir(ppy)₃) or2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin-platinum (hereinafterreferred to as PtOEP).

As an electron transport material which can be used for the electrontransport layer,2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviated toPBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazole-2-yl]benzene(abbreviated to OXD-7),3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole(abbreviated to TAZ),3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(abbreviated to p-EtTAZ), bathophenanthroline (abbreviated to BPhen),bathocuproin (abbreviated to BCP), or the like can be used, in additionto the above-mentioned metal complex such as Alq₃, Almq₃,bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviated toBAlq), BeBq₂, Zn(BOX)₂, or Zn(BTZ)₂, or a metal complex such astris(8-quinolinolato)gallium (abbreviated to Gaq₃) orbis(2-methyl-8-quinolinolato)-4-phenylphenolate-gallium (abbreviated toBGaq)

As an electron injection material for forming the electron injectionlayer, an ultrathin film of an insulating material, for example, alkalimetal halide such as LiF or CsF, alkaline earth metal halide such asCaF₂, alkali metal oxide such as Li₂O, or the like is often specificallyused. In addition, an alkali metal complex such as lithiumacetylacetonate (abbreviated to Li(acac)), 8-quinolinolato-lithium(abbreviated to Liq), or the like is also effective. A benzoxazolederivative and any one or more of alkali metal, alkaline earth metal,and transition metal may be included.

Note that the layer including a light emitting material 103 may have alaminated structure of a plurality of layers each including a lightemitting material. FIG. 12 shows an example of a laminated structure ofa plurality of layers each including a light emitting material. FIG. 12shows a structure in which a first electrode 1201, a first layerincluding a light emitting material 1202, a charge generation layer1203, a second layer including a light emitting material 1204, and asecond electrode 1205 are laminated over a substrate 1200. The chargegeneration layer 1203 needs to be formed of a highly light transmittingmaterial having a function of injecting a carrier. Although FIG. 12shows the laminated structure of the two layers each including a lightemitting material, the invention is not limited thereto. A laminatedstructure of three or more layers each including a light emittingmaterial may be used. Further, the first electrode is used as theelectrode on the substrate side; however, the second electrode may beused as the electrode on the substrate side.

Luminance is improved by using the laminated structure of layers eachincluding a light emitting material. The more layers are laminated, themore the luminance can be improved even with the same amount of current.In particular, the laminated structure of layers each including a lightemitting material is suitable for lighting use which requires highluminance. In the case of forming the laminated structure of a pluralityof layers each including a light emitting material, the layers eachincluding a light emitting material may be formed of the same materialor different materials.

For example, layers including a light emitting material formed ofmaterials which emit red (R), green (G), and blue (B) light may belaminated, so that white light emission can be obtained as a whole. Thelight-emitting layers which emit red (R), green (G), and blue (B) lightmay each be formed by an evaporation method using an evaporation mask, adroplet discharge method (also referred to as an ink-jet method), or thelike. Specifically, CuPC or PEDOT can be used for the hole injectionlayer; α-NPD, for the hole transport layer; BCP or Alq₃, for theelectron transport layer; and BCP:Li or CaF₂, for the electron injectionlayer. The light emitting layer may be formed of, for example, amaterial doped with a dopant (DCM or the like in the case of R, or DMQDor the like in the case of G) corresponding to each light emission of R,and B. In the case of obtaining white light emission, not only thelaminated structure of the light emitting materials of three colors asdescribed above but also a laminated structure of light emittingmaterials of two colors may be used. For example, white light emissioncan be obtained by laminating materials which emit blue and yellowlight.

Note that the structure of the layer including a light emitting materialis not limited to the above-described laminated structure. For example,the layer including a light emitting material may be any one of a singlelayer type, a laminated type, and a mixed type with no interface betweenlayers. A fluorescent material, a phosphorescent material, or a combinedmaterial thereof can be used. For example, a phosphorescent material canbe used for the material which emits red (R) light, and a fluorescentmaterial can be used for the materials which emit green (G) and blue (B)light. Further, any one of the following may be used: an organicmaterial including a low molecular weight material, a high molecularweight material, and an intermediate molecular weight material, aninorganic material typified by molybdenum oxide which is superior inelectron injecting properties, and a composite material of an organicmaterial and an inorganic material.

The lighting device of the invention may be formed to provide not onlywhite light but also desired-color light. A color filter, a colorconversion layer, a combination of a color filter and a color conversionlayer, or the like may be provided separately.

A second electrode 104 is formed over the layer including a lightemitting material 103. A known material can be used for the secondelectrode 104. In the case of using the second electrode 104 as acathode, a conductive material having a low work function is preferablyused. Rare earth metal such as Yb or Er can be specifically used to formthe cathode, in addition to alkali metal such as Li or Cs, alkalineearth metal such as Mg, Ca, or Sr, or an alloy including the metal(Mg:Ag, Al:Li, or the like). In the case of using an electron injectionlayer of LiF, CsF, CaF₂, Li₂O, or the like, a conductive thin film ofaluminum or the like can be used. In the case of using the secondelectrode 104 as an anode, a conductive material having a high workfunction is preferably used. Specifically, a single-layer film of TiN,ZrN, Ti, W, Ni, Pt, Cr, or the like; a laminated layer of a titaniumnitride film and a film containing aluminum as its main component; athree-layer structure of a titanium nitride film, a film containingaluminum as its main component, and a titanium nitride film; or the likecan be used. Alternatively, the second electrode may be formed bylaminating a transparent conductive film over a reflective electrode ofTi, Al, or the like.

An insulating film 105 is formed to cover the second electrode 104 andthe layer including a light emitting material 103. The insulating film105 electrically insulates the first electrode 102 and the secondelectrode 104 from the second electrode 104 and an auxiliary electrode106, respectively. Note that the insulating film 105 may have a functionas a protective film for preventing penetration of a substance, such asmoisture and oxygen, to be the cause of promoting deterioration of thelayer including a light emitting material.

The insulating film 105 has an opening 107, through which the firstelectrode 102 is electrically connected to the auxiliary electrode 106.A low-resistivity material is preferably used for the auxiliaryelectrode 106; specifically, a material such as aluminum, copper, orsilver can be used. The diameter of the opening may be 10 μm to 500 μm,preferably, 50 μm to 200 μm.

A plurality of the openings 107 is provided in a light emitting region108. An effect of voltage drop due to relatively high resistivity of thetransparent conductive film can be reduced by electrically connectingthe auxiliary electrode 106 to the first electrode 102 through theopening 107. In other words, the auxiliary electrode 106 practicallylowers the resistivity of the first electrode 102 by being electricallyconnected to the first electrode 102 through the plurality of openings107 formed in the light emitting region 108. This can reducenonuniformity of luminance in which a portion away from a current supplyterminal is dark. In the case where the size of the opening issufficiently small, the presence of the auxiliary electrode can be, forthe most part, disregarded when the lighting device is seen from theside of light emission, in other words, from the side of the lighttransmitting substrate. Since the auxiliary electrode is not placed inthe direction of light emission, a material, a thickness, or a formationposition of the auxiliary electrode can be freely set. Therefore, theauxiliary electrode can be selectively formed in a position wherevoltage tends to drop, or can be entirely formed over the light emittingregion of the lighting device.

Since the lighting device of the invention can reduce the nonuniformityof luminance due to voltage drop caused by relatively high resistivityof the first electrode, a lighting device having favorable in-planeuniformity of luminance can be obtained. Specifically, the lightingdevice is preferably applied to a large-sized lighting device.

Embodiment Mode 2

A structure of a lighting device of the invention is described withreference to FIGS. 5A and 5B. A lighting device shown in FIGS. 5A and 5Bis a top emission lighting device which emits light from the oppositeside of a substrate side. Note that FIG. 5B is a top view of a lightemitting region of a lighting device and FIG. 5A is a cross-sectionalview (taken along line A-A′ in FIG. 5B) of the vicinity of an opening inthe light emitting region.

In FIGS. 5A and 5B, a thin substrate formed of a flexible material isused as a substrate 501. Specifically, a flexible substrate such as aplastic substrate, more specifically a polyester film or an acrylicresin film, can be used.

A second electrode 502 is formed over the substrate 501. A knownmaterial can be used for the second electrode 502. In the case of usingthe second electrode 502 as a cathode, a conductive material having alow work function is preferably used. Rare earth metal such as Yb or Ercan be used to form the cathode, in addition to alkali metal such as Lior Cs, alkaline earth metal such as Mg, Ca, or Sr, or an alloy includingthe metal (Mg:Ag, Al:Li, or the like). In the case of using an electroninjection layer of LiF, CsF, CaF₂, or Li₂O, a typical conductive thinfilm of aluminum or the like can be used. In the case of using thesecond electrode 502 as an anode, a conductive material having a highwork function is preferably used. Specifically, a single-layer film ofTiN, ZrN, Ti, W, Ni, Pt, Cr, or the like; a laminated layer of atitanium nitride film and a film containing aluminum as its maincomponent; a three-layer structure of a titanium nitride film, a filmcontaining aluminum as its main component, and a titanium nitride filmcan be used. Alternatively, the second electrode may be formed bylaminating a transparent conductive film over a reflective electrode ofTi, Al, or the like.

A layer including a light emitting material 503 is formed over thesecond electrode 502. A known material can be used for the layerincluding a light emitting material 503, and either a low molecularweight material or a high molecular weight material can be used. Amaterial for forming, the layer including a light emitting material mayinclude not only the one formed of only an organic compound material butalso the one partly containing an inorganic compound. The layerincluding a light emitting material is formed by appropriately combininga hole injection layer, a hole transport layer, a hole blocking layer, alight emitting layer, an electron transport layer, an electron injectionlayer, or the like. The layer including a light emitting material may bea single layer or have a laminated structure of a plurality of layers.

Note that the layer including a light emitting material 503 may have alaminated structure of a plurality of layers each including a lightemitting material. Luminance is improved by using the laminatedstructure of layers each including a light emitting material. The morelayers are laminated, the more the luminance can be improved even withthe same amount of current. In particular, the laminated structure oflayers each including a light emitting material is suitable for lightinguse which requires high luminance. In the case of forming the laminatedstructure of a plurality of layers each including a light emittingmaterial, the layers each including a light emitting material may beformed of the same material or different materials.

A transparent conductive film is formed over the layer including a lightemitting material 503 as a first electrode 504. For example, indium tinoxide (hereinafter referred to as ITO), indium tin oxide containingsilicon, indium oxide containing zinc oxide (ZnO) of 2% to 20%, or thelike can be used for the transparent conductive film.

The substrate 501, the second electrode 502, the layer including a lightemitting material 503, and the first electrode 504 have an opening 507.An insulating film 505 is formed to cover the vicinity of the opening ofthe first electrode 504 and the substrate 501 and a side wall of theopening. The insulating film 505 electrically insulates the firstelectrode 504 and the second electrode 502 from the second electrode 502and an auxiliary electrode 506, respectively. Note that the insulatingfilm 505 may have a function as a protective film for preventingpenetration of a substance, such as moisture and oxygen, to be the causeof promoting deterioration of the layer including a light emittingmaterial.

The auxiliary electrode 506 is formed over a lower surface of thesubstrate, in the opening, and in the vicinity of the opening of thefirst electrode, and is electrically connected to the first electrode inthe vicinity of the opening. A low-resistivity material is preferablyused for the auxiliary electrode 506; specifically, a material such asaluminum, copper, or silver can be used. The diameter of the opening maybe 10 μm to 500 μm, preferably, 50 μm to 200 μm.

A plurality of the openings 507 is provided in a light emitting region508. An effect of voltage drop due to relatively high resistivity of thetransparent conductive film can be reduced by electrically connectingthe auxiliary electrode 506 to the first electrode 504 through theopening 507. In other words, the auxiliary electrode 506 practicallylowers the resistivity of the first electrode 504 by being electricallyconnected to the first electrode 504 through the plurality of theopenings 507 formed in the light emitting region 508. This can reducenonuniformity of luminance in which a portion away from a current supplyterminal is dark. In the case where the size of the opening issufficiently small, the presence of the auxiliary electrode can be, forthe most part, disregarded when the lighting device is seen from theside of light emission, in other words, from the side of a lighttransmitting substrate. Since the auxiliary electrode is not placed inthe direction of light emission, a material, a thickness, or a formationposition of the auxiliary electrode can be freely set. Therefore, theauxiliary electrode can be selectively formed in a position wherevoltage tends to drop, or can be entirely formed over the light emittingregion of the lighting device.

Since the lighting device of the invention can reduce in-planenonuniformity of luminance which is caused by voltage drop due torelatively high resistivity of the first electrode, a lighting devicehaving favorable in-plane uniformity of luminance can be obtained.Specifically, the lighting device is preferably applied to a large-sizedlighting device.

Embodiment 1

A method for manufacturing the lighting device of the invention shown inFIGS. 1A and 1B is described in this embodiment with reference to FIGS.2A to 2D.

A transparent conductive film serving as a first electrode 202 is formedover a light transmitting substrate 201. In this embodiment, a glasssubstrate is used as the light transmitting substrate 201 and an ITOfilm is formed for forming the first electrode 202.

A layer including a light emitting material 203 is formed over the firstelectrode 202. A known material can be used for the layer including alight emitting material 203. The layer including a light emittingmaterial may have a laminated structure of a plurality of layers eachincluding a light emitting material.

A second electrode 204 is formed over the layer including a lightemitting material 203 (FIG. 2A). The second electrode 204 has anopening. After the second electrode is entirely formed over the layerincluding a light emitting material, the opening may be formed bypattering the second electrode by a photolithography method.Alternatively, the second electrode 204 having the opening may be formedby using a mask. In this embodiment, an aluminum film is used as thesecond electrode 204. After the second electrode is entirely formed overthe layer including a light emitting material 203, it is patterned by aphotolithography method. Thereafter, the opening is formed in the layerincluding a light emitting material, using the patterned secondelectrode as a mask (FIG. 2B).

An insulating film 205 is formed to cover the layer including a lightemitting material 203 and the second electrode 204 (FIG. 2C). Theinsulating film 205 also has an opening. After the insulating film isentirely formed, the opening may be formed by patterning the insulatingfilm by a photolithography method. Alternatively, the insulating filmmay be formed by using a mask. In this embodiment, a silicon oxide filmis used as the insulating film 205.

An auxiliary electrode 206 is formed (FIG. 2D). The auxiliary electrode206 preferably has low resistivity, and aluminum is used in thisembodiment. The auxiliary electrode 206 is electrically connected to thefirst electrode 202 through an opening 207 and insulated from the secondelectrode 204.

Thus, the ITO film serving as the first electrode 202 is connected tothe auxiliary electrode 206 through the opening 207, and an effect ofvoltage drop due to relatively high resistivity of the first electrodecan be reduced. Therefore, in-plane nonuniformity of luminance can bereduced when the lighting device is applied to a large-sized lightingdevice. In the case where the opening 207 is sufficiently small, thepresence of the auxiliary electrode can be, for the most part,disregarded when the lighting device is seen from the side of lightemission, in other words, from the side of the light transmittingsubstrate.

In this embodiment, the layer including a light emitting material isentirely formed and then patterned using aluminum as a mask. However,the layer including a light emitting material may be formed using a maskto have an opening.

FIGS. 3A to 3C show a method for forming each of a layer including alight emitting material 303 and a second electrode 304 using a mask. Inother words, each of the layer including a light emitting material 303and the second electrode 304 is formed using a mask after a firstelectrode 302 is entirely formed. An insulating film 305, an auxiliaryelectrode 306, and an opening 307 may be formed by a similar method tothe above-described method. At this time, the first electrode is morecertainly insulated from the second electrode by making the opening ofthe second electrode 304 larger than that of the layer including a lightemitting material 303.

Embodiment 2

A method for manufacturing the lighting device of the invention shown inFIGS. 1A and 1B, which is different from that of Embodiment 1, isdescribed in this embodiment with reference to FIGS. 4A to 4C.

A transparent conductive film serving as a first electrode 402 is formedover a light transmitting substrate 401. In this embodiment, a glasssubstrate is used as the light transmitting substrate 401 and an ITOfilm is formed as the first electrode 402.

A layer including a light emitting material 403 and a second electrode404 are sequentially formed (FIG. 4A). In this embodiment, an aluminumfilm is formed for the second electrode 404.

Then, laser light is emitted to the light transmitting substrate 401side to form an opening (FIG. 4B). As the laser light, used is laserlight with a wavelength enough to be transmitted through the glasssubstrate and ITO and absorbed by the layer including a light emittingmaterial 403 and the second electrode 404. In this embodiment, laserlight with a wavelength of 532 nm is used. The laser light with awavelength of 532 nm can be obtained by converting a fundamental wave(wavelength: 1064 nm) of a YAG laser, YVO₄, or the like into a secondharmonic by a nonlinear optical element. The layer including a lightemitting material and the second electrode after absorbing the laserlight are heated and sublimed, thereby forming the opening. After theopening is formed, an insulating film 405 and an auxiliary electrode 406are formed as in Embodiment 1 so that the first electrode 402 iselectrically connected to the auxiliary electrode 406 through theopening 407 (FIG. 4C).

Embodiment 3

A method for manufacturing the lighting device of the invention shown inFIGS. 5A and 5B is described in this embodiment with reference to FIGS.6A to 6C and FIGS. 7A and 7B.

A second electrode 602, a layer including a light emitting material 603,and a first electrode 604 are formed over a thin substrate 601 formed ofa flexible material. In this embodiment, an aluminum film is formed asthe second electrode 602 and an ITO film is formed as the firstelectrode 604 over a polyester film (FIG. 6A).

The substrate 601, the second electrode 602, the layer including a lightemitting material 603, and the first electrode 604 are provided with anopening (FIG. 6B). Since the substrate 601 is formed of a flexiblematerial, the opening can be easily formed by applying physical force.

A silicon oxide film is formed as an insulating film 605. The siliconoxide film is formed using a mask by a sputtering method or anevaporation method (FIG. 6C). The silicon oxide film is also formed towrap around to the opposite surface of an intended surface through theopening by using a sputtering method or an evaporation method. Accordingto this, the second electrode 602 is more certainly insulated from anauxiliary electrode 606.

The auxiliary electrode 606 is formed. First, silver is deposited on thefirst electrode 604 side by a printing method. With the use of aprinting method at this time, the opening 607 is filled with silver(FIG. 7A). Then, silver is entirely deposited on the substrate 601 side(FIG. 7B). According to this, the first electrode 604 is electricallyconnected to the auxiliary electrode 606. Thus, an effect of voltagedrop due to relatively high resistivity of the first electrode can bereduced. Therefore, a lighting device having favorable in-planeuniformity of luminance can be obtained when the lighting device isapplied to a large-sized lighting device.

In the structure of this embodiment, an ITO film serving as the firstelectrode is connected to the auxiliary electrode formed of silver, on alight emitting side. However, in the case where the opening 607 issufficiently small, the presence of the auxiliary electrode can be, forthe most part, disregarded when the lighting device is seen from theside of light emission, in other words, from the side of the firstelectrode.

Embodiment 4

An example of an overall structure of a lighting device of the inventionis described in this embodiment with reference to FIGS. 8A and 8B.

FIGS. 8A and 8B are a top view and a cross-sectional view of a lightingdevice of the invention, respectively. The lighting device of theinvention includes a substrate 801, a first electrode 802, a layerincluding a light emitting material 803, a second electrode 804, aninsulating film 805, and an auxiliary electrode 806. The first electrode802 is electrically connected to the auxiliary electrode 806 through anopening 807. A plurality of the openings 807 is provided in a lightemitting region. A second insulating film 808 is at the end of the lightemitting region, which serves to prevent the first electrode 802 and thesecond electrode 804 from shorting. Current supply terminals 809 areeach connected to the second electrode 804 and the auxiliary electrode806. The light emitting region is sealed with a sealant 810. The sealantis preferably a material which let penetrate as little moisture andoxygen as possible to prevent deterioration of the layer including alight emitting material. A space 811 surrounded by the sealant is filledwith a filler. The space 811 surrounded by the sealant may be filledwith an inert gas (nitrogen, argon, or the like) in place of the filler.Alternatively, the space may be filled with a sealant.

FIGS. 8A and 8B show the structure described in Embodiment 1 as anexample; however, the structure described in Embodiment 2 or 3 can alsobe used as a lighting device by sealing similarly.

Embodiment 5

Examples of a device using a lighting device of the invention aredescribed in this embodiment with reference to FIG. 9 and FIGS. 10A to10C.

FIG. 9 shows an example of a liquid crystal display device using alighting device of the invention as a backlight. The liquid crystaldisplay device shown in FIG. 9 includes a chassis 901, a liquid crystallayer 902, a backlight 903, and a chassis 904. The liquid crystal layer902 is connected to a driver IC 905. The lighting device of theinvention is used as the backlight 903 and current is supplied through aterminal 906.

A backlight having favorable in-plane uniformity of luminance can beobtained by using the lighting device of the invention as a backlight ofa liquid crystal display device; thus, high quality of a display deviceis obtained. Since the backlight can have large area, the liquid crystaldisplay device can also have large area. Further, the light emittingelement is thin and consumes low power; therefore, the display devicecan also be thinned and made to consume low power.

FIG. 10A shows the lighting device of the invention used as indoorlighting. The lighting device of the invention is a surface-emittinglighting device and has favorable in-plane uniformity of luminance evenwhen it has large area. Therefore, an entire ceiling, for example, canbe provided with the lighting device of the invention. Not only theceiling but also a wall, a floor, or a column can be provided with thelighting device of the invention. Further, the lighting device of theinvention can be provided on a curved surface because the lightingdevice is flexible. Moreover, the lighting device can be used not onlyindoors but also outdoors and can be provided on a building wall or thelike as an outdoor light.

FIG. 10B shows the lighting device of the invention used as lighting ina tunnel. The lighting device of the invention can be formed along acurved inner wall of a tunnel because the lighting device is flexible.

FIG. 10C shows an example of the lighting device of the invention usedas interior lighting. Since the lighting device of the invention is thinand flexible and is a surface-emitting type, it can be processed into adesired shape as shown in FIG. 10B.

The lighting device of the invention can also be used for lighting intaking a picture. In the case of taking a picture, a picture similar toone taken with a subject illuminated by natural light can be taken whena subject is illuminated by large-sized light with uniform luminance.

1. A lighting device comprising: a first electrode over a substrate; alayer including a light emitting material over the first electrode; asecond electrode over the layer including a light emitting material; athird electrode over the first electrode, and electrically connected tothe first electrode; and an insulating layer over the first electrode,and between the layer including a light emitting material and the thirdelectrode, wherein the third electrode is isolated from the secondelectrode and the layer including a light emitting material, wherein thelayer including a light emitting material comprises: a first layerincluding a first light emitting material; a second layer including asecond light emitting material; and a charge generation layer providedbetween the first layer and the second layer, and wherein a resistivityof the third electrode is lower than that of the first electrode.
 2. Alighting device according to claim 1, wherein the first electrodecomprises a transparent conductive film.
 3. A lighting device accordingto claim 1, wherein the first electrode comprises a substance selectedfrom the group consisting of indium tin oxide, indium tin oxideincluding silicon, and indium oxide including zinc oxide.
 4. A lightingdevice according to claim 1, wherein the first electrode comprises asubstance selected from the group consisting of indium tin oxide, indiumtin oxide including silicon, and indium oxide including zinc oxide.
 5. Alighting device according to claim 1, wherein the first electrodecomprises a substance selected from the group consisting of indium tinoxide, indium tin oxide including silicon, and indium oxide includingzinc oxide.
 6. A lighting device according to claim 1, wherein the layerincluding a light emitting material comprises an organic compound or aninorganic compound.
 7. A lighting device according to claim 1, whereinthe insulating layer comprises a substance selected from the groupconsisting of siloxane, acrylic and polyimide.
 8. A lighting deviceaccording to claim 1, wherein the third electrode comprises a substanceselected from the group consisting of aluminum and copper.
 9. A lightingdevice according to claim 1, wherein the lighting device emits whitelight.
 10. A lighting device comprising: a first electrode over asubstrate; a layer including a light emitting material over the firstelectrode; a second electrode over the layer including a light emittingmaterial; a third electrode over the first electrode, and electricallyconnected to the first electrode; and an insulating layer over the firstelectrode, and between the layer including a light emitting material andthe third electrode, wherein the third electrode is isolated from thesecond electrode and the layer including a light emitting material,wherein the layer including a light emitting material comprises: a firstlayer including a first light emitting material; a second layerincluding a second light emitting material over the first layer; and athird layer including a third light emitting material over the secondlayer, and wherein a resistivity of the third electrode is lower thanthat of the first electrode.
 11. A lighting device according to claim10, wherein the first electrode comprises a transparent conductive film.12. A lighting device according to claim 10, wherein the layer includinga light emitting material comprises an organic compound or an inorganiccompound.
 13. A lighting device according to claim 10, wherein theinsulating layer comprises a substance selected from the groupconsisting of siloxane, acrylic and polyimide.
 14. A lighting deviceaccording to claim 10, wherein the third electrode comprises a substanceselected from the group consisting of aluminum and copper.
 15. Alighting device according to claim 10, wherein the lighting device emitswhite light.
 16. A lighting device comprising: a first electrode over asubstrate; a layer including a light emitting material over the firstelectrode; a second electrode over the layer including a light emittingmaterial; a third electrode over the first electrode, and electricallyconnected to the first electrode; and an insulating layer over the firstelectrode, and between the layer including a light emitting material andthe third electrode, wherein the third electrode is isolated from thesecond electrode and the layer including a light emitting material,wherein a resistivity of the third electrode is lower than that of thefirst electrode, and wherein the insulating layer is in contact with thefirst electrode, the layer including a light emitting material, and thesecond electrode.
 17. A lighting device according to claim 16, whereinthe first electrode comprises a transparent conductive film.
 18. Alighting device according to claim 16, wherein the layer including alight emitting material comprises an organic compound or an inorganiccompound.
 19. A lighting device according to claim 16, wherein theinsulating layer comprises a substance selected from the groupconsisting of siloxane, acrylic and polyimide.
 20. A lighting deviceaccording to claim 16, wherein the third electrode comprises a substanceselected from the group consisting of aluminum and copper.
 21. Alighting device according to claim 16, wherein the lighting device emitswhite light.
 22. A lighting device comprising: a first electrode over asubstrate; a layer including a light emitting material over and incontact with the first electrode; a second electrode over and in contactwith the layer including a light emitting material; a third electrodeover and in contact with the first electrode; and an insulating layerbetween the layer including a light emitting material and the thirdelectrode, wherein the insulating layer is in contact with the layerincluding a light emitting material and the third electrode, and whereina resistivity of the third electrode is lower than that of the firstelectrode.
 23. A lighting device according to claim 22, wherein thefirst electrode comprises a transparent conductive film.
 24. A lightingdevice according to claim 22, wherein the first electrode comprises asubstance selected from the group consisting of indium tin oxide, indiumtin oxide including silicon, and indium oxide including zinc oxide. 25.A lighting device according to claim 22, wherein the layer including alight emitting material comprises an organic compound or an inorganiccompound.
 26. A lighting device according to claim 22, wherein theinsulating layer comprises a substance selected from the groupconsisting of siloxane, acrylic and polyimide.
 27. A lighting deviceaccording to claim 22, wherein the third electrode comprises a substanceselected from the group consisting of aluminum and copper.
 28. Alighting device according to claim 22, wherein the lighting device emitswhite light.
 29. A lighting device comprising: a first electrode over asubstrate; a layer including a light emitting material over and incontact with the first electrode; a second electrode over and in contactwith the layer including a light emitting material; a third electrodeover and in contact with the first electrode; and an insulating layerbetween the layer including a light emitting material and the thirdelectrode, wherein the insulating layer is in contact with the layerincluding a light emitting material and the third electrode, wherein thelayer including a light emitting material comprises: a first layerincluding a first light emitting material; a second layer including asecond light emitting material over the first layer; and a third layerincluding a third light emitting material over the second layer, andwherein a resistivity of the third electrode is lower than that of thefirst electrode.
 30. A lighting device according to claim 29, whereinthe first electrode comprises a transparent conductive film.
 31. Alighting device according to claim 29, wherein the first electrodecomprises a substance selected from the group consisting of indium tinoxide, indium tin oxide including silicon, and indium oxide includingzinc oxide.
 32. A lighting device according to claim 29, wherein thelayer including a light emitting material comprises an organic compoundor an inorganic compound.
 33. A lighting device according to claim 29,wherein the insulating layer comprises a substance selected from thegroup consisting of siloxane, acrylic and polyimide.
 34. A lightingdevice according to claim 29, wherein the third electrode comprises asubstance selected from the group consisting of aluminum and copper. 35.A lighting device according to claim 29, wherein the lighting deviceemits white light.
 36. A lighting device comprising: a first electrodeover a substrate; a layer including a light emitting material over andin contact with the first electrode; a second electrode over and incontact with the layer including a light emitting material; a thirdelectrode over and in contact with the first electrode; an insulatinglayer between the layer including a light emitting material and thethird electrode; and a sealant over the third electrode; wherein theinsulating layer is in contact with the layer including a light emittingmaterial and the third electrode, wherein a resistivity of the thirdelectrode is lower than that of the first electrode.
 37. A lightingdevice according to claim 36, wherein the first electrode comprises atransparent conductive film.
 38. A lighting device according to claim36, wherein the first electrode comprises a substance selected from thegroup consisting of indium tin oxide, indium tin oxide includingsilicon, and indium oxide including zinc oxide.
 39. A lighting deviceaccording to claim 36, wherein the layer including a light emittingmaterial comprises an organic compound or an inorganic compound.
 40. Alighting device according to claim 36, wherein the insulating layercomprises a substance selected from the group consisting of siloxane,acrylic and polyimide.
 41. A lighting device according to claim 36,wherein the third electrode comprises a substance selected from thegroup consisting of aluminum and copper.
 42. A lighting device accordingto claim 36, wherein the lighting device emits white light.